1. custom optional field in Maniphest

cannot customize workboard items to show the custom fields on the preview - T4863

2. countdown event

We embed those in task description with Cxx syntax (with previous creation of the countdown itself)

Pros:

can see all the deadlines in one place and filter them out

Cons:

very bulky creation

it's stress inducing to see that clock ticking :D

3. calendar entries

Create calendar entries and attach project tags to them, and embed them as well to the task via Exx syntax.

Pros and cons are a bit of mix between 1 and 2.

Milestone subprojects + Countdown are great to communicate high level goals, ie. some 3 month target we're trying to hit but this is on a single task level thingy.

I know that this has been discussed a lot and there are some solutions which partially fix the problem but none provide the flexibility and a nice UX for the one creating the task and for the owner to see their deadlines, etc.

It seems that T4863 might be the solution to some of these problems (easier visibility of due dates on tasks), but after it, the problem remains of not being able to query the task in the phabricator interface by custom field (#no 1 option in this list).